cursors / primary key / trigger / view questions

Types of cursors in SQL ?

* Static
* Dynamic
* Forward-only
* Keyset-driven

What is a “primary key”?

Primary Key is a type of a constraint enforcing uniqueness and data integrity for each row of a table. All columns participating in a primary key constraint must possess the NOT NULL property.For example “user Id” should be unique for users, so we can make that field a s primary key in some tables for making sure that value wont repeat.

What is a “trigger”?

Triggers are stored procedures
created in order to enforce integrity rules in a database. A trigger is executed every time a data-modification operation occurs (i.e., insert, update or delete). Triggers are executed automatically on occurrence of one of the data-modification operations. A trigger is a database object directly associated with a particular table. It fires whenever a specific statement/type of statement is issued against that table. The types of statements are insert,update,delete and query statements. Basically, trigger is a set of SQL statements A trigger is a solution to the restrictions of a constraint.

What is “index covering” of a query?
Index covering means that “Data can be found only using indexes, without touching the tables”

What is a SQL view?

An output of a query can be stored as a view. View acts like small table which meets our criterion. View is a precomplied SQL query which is used to select data from one or more tables. A view is like a table but it doesn’t physically take any space. View is a good way to present data in a particular format if you use that query quite often. View can also be used to restrict users from accessing the tables directly.Its mainly used to view the data from various tables.

What is blocking and when it is happening?

Blocking happens when one connection from an application holds a lock and a second connection requires a conflicting lock type. This forces the second connection to wait, blocked on the first.

How do you implement one-to-one, one-to-many and many-to-many relationships while designing tables?

One-to-One relationship can be implemented as a single table and rarely as two tables with primary and foreign key relationships.One-to-Many relationships are implemented by splitting the data into two tables with primary key and foreign key relationships.Many-to-Many relationships are implemented using a junction table with the keys from both the tables forming the composite primary key of the junction table.